What is concrete?

Concrete consists of a mix of ingredients, including Portland cement, pozzolans, water, coarse aggregates, fine aggregates, and additives. Concrete may also contain mineral colors, granulated blast-furnace slag, and blended cements. When fresh, concrete can be molded hours after production. Once the initial set time is reached, concrete continues to gain strength.

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Why is concrete gray?

Concrete can be ordered in many colors, but its natural gray hue arises because of the gray color of the cement typically used in its production. This coloration of cement is due to the presence of Iron Ore, which is black in its natural state. During the manufacturing of Portland Cement, Iron Ore is combined and melted with other materials, tinting the cement gray.

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How is the strength of concrete measured?

Scientists measure the strength of concrete using compression and flexural mechanical strength tests. The strength depends significantly on the water-cement ratio, as well as the quality of aggregates and paste in the cement.

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Are there quality standards for concrete?

Yes, concrete must adhere to local building codes as well as standards set by ACI (American Concrete Institute) and ASTM (American Society for Testing and Materials).

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What is the difference between cement and concrete?

Concrete is used for finished products like sidewalks and foundations. It contains sand, gravel, and cement. Cement, which is the gray powder hardening ingredient, typically consists of 60% lime (limestone), 25% silica, 5% alumina, and other materials such as gypsum and iron oxide.

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How is concrete measured?

Concrete is measured by the cubic yard, which equals 27 cubic feet (three feet by three feet by three feet). Normal concrete weighs about 4,000 pounds per cubic yard.

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Does concrete gain strength by drying out?

No, concrete gains strength through a chemical reaction called hydration, which starts when water is mixed with cement. Hydration continues for weeks to months, but once concrete dries completely, hydration stops, and it no longer gains strength.
 

Industrial/Commercial Questions about Concrete

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What types of concrete does LBC offer?

LBC offers various high-quality products including Performance Concrete, Durable Concrete, High Strength Concrete, Pavement Concrete, Lightweight and Heavyweight Concrete, Grouts, Architectural Concrete, and Customized Concrete.

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Is there an average going price per cubic yard of concrete?

Concrete prices vary by city and region. It's best to contact a local ready-mix concrete company for an estimate.

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What is fly ash?

Fly ash is a byproduct of coal combustion, commonly produced by coal-fired electrical generating facilities. It is a cementitious material, meaning it possesses properties that cause it to harden upon exposure to water. Typically, fly ash does not develop significant compressive strength on its own. However, when combined with Portland Cement, fly ash can acquire strength characteristics very similar to cement. Fly ash reacts with a chemical by-product of cement hydration known as calcium hydroxide (CaOH), which can otherwise cause detrimental effects in concrete such as increased porosity and efflorescence—formation of calcium carbonate crystals on the concrete or mortar surface. By reacting with calcium hydroxide to form additional calcium silicate hydrate, a binder derivative of cement, fly ash enhances the strength of concrete and mitigates potentially harmful effects. Fly ash is particularly advantageous in hot weather conditions as it tends to reduce heat generation during concrete curing.
 

Residential Questions About Concrete

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What strength concrete is normally used for the slab under a home?

Typical mixes range from 2500 pounds per square inch (psi) to 3000 psi, depending on the geography of the country and the quality of the raw materials. Sometimes we are asked if a different weight should be used for the garage area. This is not really necessary. Usually the biggest load on a slab is the heaving from the sub grade and not the structure on top of it.
 

How do I remove glue from concrete before staining?

Identify the type of glue used and consult a flooring supplier for the appropriate removal method. Once the glue is removed, you can stain the concrete if it hasn't been previously sealed.

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How do I stain/paint my concrete floor?

Visit a paint store for concrete stain or paint. Discuss your desired look and functionality with the staff for suitable recommendations.

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My concrete is cracking after only a short time. Is there something wrong with it and can it be repaired?

All concrete cracks. It contracts during the drying, curing, and hardening process because the bond between the cement paste and aggregates isn't always strong enough to withstand this stress. The best method to prevent unsightly cracking is to incorporate joints at regular intervals. A practical guideline is to measure the slab's depth and multiply it by three to determine the approximate spacing between joints. For instance, a 4-inch concrete slab should have joints spaced every 10 to 12 feet. Additionally, uneven shifting of the subgrade or substructure can lead to cracking, indicating a structural issue rather than improper curing or joint placement. It's crucial to identify and address the root cause of any cracking before attempting repairs. Epoxy grout is highly effective for repairing concrete cracks.

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My concrete has oil/grease stains. How can I get rid of them?

• Commercial products are available in paint/hardware home centers.

• Sprinkle with tri-sodium phosphate. Allow to stand for 30 minutes, then scrub with a stiff brush and hot water. Rinse with clean water.

• Scrub stain with concentrated detergent using a stiff brush. Rinse well with water. Dry and repeat if necessary.

• Sprinkle dishwasher detergent on wet concrete. Let it stand a few minutes, then pour boiling water on the area. Scrub and rinse.

• Dissolve a cup tri-sodium phosphate in 1 gallon of hot water. Pour over stained concrete surface and allow soaking for 25 minutes. Scrub with stiff brush or broom. Rinse with clean water. Repeat if necessary.
  
   

How long should I cure my concrete?

This question can only be answered by the professionals associated with the project. Concrete cures at different rates depending on the constituent ingredients and the ambient conditions it is exposed to. Your contractor (concrete supplier) should know what sort of curing is required for the particular mix being used. Also, by following their recommendation, you can maintain whatever warranty might be associated with the work performed.

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If you have other questions about concrete, contact LBC today.